Application of metasurface-enhanced infra-red spectroscopy to distinguish between normal and cancerous cell types.

Fourier transform infrared (FTIR) spectra of biological cells can reveal clinically important information about cells' composition, including their normal or cancerous status. The recently emerged diagnostic technique of spectral cytopathology (SCP) combines FTIR with multivariate statistical analysis to detect cell abnormalities, differentiate between cell types, and monitor disease progression. We demonstrate a new variant of SCP, a metasurface-enhanced infrared reflection spectroscopic cytopathology (MEIRSC) that utilises judiciously designed plasmonic metasurfaces to localize and enhance the evanescent field near the cell's membrane, and to carry out spectroscopic interrogations of the cells attached to the metasurface using reflected infrared light. Our findings indicate that the MEIRSC approach enables us to differentiate between normal and cancerous human colon cells. The sensitivity of MEIRSC is such that a very small (about 50 nm deep) portion of the cell can yield valuable diagnostic information.

Experimental demonstration of the microscopic origin of circular dichroism in two-dimensional metamaterials.

Optical activity and circular dichroism are fascinating physical phenomena originating from the interaction of light with chiral molecules or other nano objects lacking mirror symmetries in three-dimensional (3D) space. While chiral optical properties are weak in most of naturally occurring materials, they can be engineered and significantly enhanced in synthetic optical media known as chiral metamaterials, where the spatial symmetry of their building blocks is broken on a nanoscale. Although originally discovered in 3D structures, circular dichroism can also emerge in a two-dimensional (2D) metasurface. The origin of the resulting circular dichroism is rather subtle, and is related to non-radiative (Ohmic) dissipation of the constituent metamolecules. Because such dissipation occurs on a nanoscale, this effect has never been experimentally probed and visualized. Using a suite of recently developed nanoscale-measurement tools, we establish that the circular dichroism in a nanostructured metasurface occurs due to handedness-dependent Ohmic heating.